Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Swimming algae offer Penn researchers insights into living fluid dynamics

08.04.2015

None of us would be alive if sperm cells didn't know how to swim, or if the cilia in our lungs couldn't prevent fluid buildup. But we know very little about the dynamics of so-called "living fluids," those containing cells, microorganisms or other biological structures.

"Living fluids are found everywhere, from vaccines to yogurt to biofuels," said Paulo Arratia, an associate professor in the Department of Mechanical Engineering and Applied Mechanics in the University of Pennsylvania School of Engineering and Applied Science. "We just don't usually think about them in that sense. We'd like to develop knowledge about how they flow and behave, the same way we've developed it for nonliving fluids."


This image shows algae swimming on a 30 micron thin liquid film that rests in the middle of a wire frame scaffold.

Credit: University of Pennsylvania

Understanding the behavior of living fluids starts with understanding the swimmers themselves. With that goal in mind, Arratia's lab group conducted a study examining the swimming dynamics of Chlamydomonas reinhardtii, a unicellular green alga that propels itself with two whip-like flagella, in fluids exhibiting a range of properties.

The researchers discovered that C. reinhardtii changes its swim stroke dramatically in elastic fluids, those with both liquid and solid-like properties, compared with non-elastic, or Newtonian, fluids.

"This algae's flagellum has the same biological structure as the cilia in our lungs," Arratia said. "We hope this can become a model for how the lungs move mucus, a fluid which possesses elasticity."

Such a model may help researchers to understand and treat lung diseases that involve excessive fluid buildup, including cystic fibrosis.

Graduate student Boyang Qin was lead author on the study, published in Nature Scientific Reports, which also included contributions from current and former mechanical engineering postdoctoral researchers Arvind Gopinath and Jin Yang, as well as Jerry Gollub, a professor of physics at Haverford University.

Most of our understanding of microbial swimming patterns comes from studies conducted in water. Yet many of the fluids we encounter in our everyday lives are much more viscous than water. Viscous fluids that contain chain-like molecules known as polymers are also elastic, meaning they possess both liquid and solid-like behavior. These so-called "viscoelastic fluids" include familiar household items such as yogurt, toothpaste and lotion. Despite the ubiquity of complex fluids, the consequences of viscosity and elasticity for the physics of swimming are not well understood.

"Many environments that microbes swim in, such as soil, mucus and tissue, are not just plain water but contain particles and polymers," Arratia said. "We're interested in learning how organisms behave in these more complex and realistic environments."

To do so, the researchers set up experiments to examine the effects of viscosity and elasticity on the swimming behavior of C. reinhardtii, a common model organism. They prepared Newtonian solutions that spanned a 10-fold range of viscosities by dissolving a sugar-like compound in water. They also prepared viscoelastic solutions that spanned a 50-fold range in elasticity, by dissolving small amounts of a polymer in water. They then suspended samples of C. reinhardtii in each solution and captured the alga's swimming behavior using a microscope equipped with a high-speed camera. The images were then analyzed to assess how the fluid media influenced both the beating frequency of C. reinhardtii's flagella and the shape of its swim stroke.

As viscosity increased for Newtonian fluids, the researchers observed a decrease in beating frequency. This result was intuitive: a person, for instance, would swim more slowly in a pool of honey than in a pool of water.

While the alga's flagella beat faster when the viscosity of Newtonian solutions was increased, the overall shape of the swim stroke did not change. This, however, was in sharp contrast to what they observed in viscoelastic solutions.

"Once you add a little elasticity, the stroke shape becomes completely different," said Gopinath. "On top of that, we were surprised to find that, when we increased elasticity, the beating frequency became much higher."

The reason C. reinhardtii changes its swim pattern so dramatically in elastic fluids is not yet clear. One potential explanation is that the polymers present in elastic fluids are deforming the microbes, producing additional stress forces.

"Extra stresses imparted by the polymers can restrain the way you swim, changing the shape of your stroke," said Qin. "But the increase in beat frequency is still a bit of a mystery."

That mystery is an ongoing area of exploration. One future step for Arratia's research team will be to tease out whether the faster beating of flagella in elastic fluids is a passive response, or if the microbes are actively modifying their behavior to the environment.

"When you swim, you know if you're actively adapting to the fluid," Arratia said. "Likewise what we're seeing here could be an adaptive response, but it could also be that the flagella's motion is being actuated by the liquid."

Separating the two possibilities is important when considering artificial swimmers, such as micro-robots, which may in the future be deployed within the human body to deliver drugs or target disease. If researchers want to predict the patterns of an artificial swimmer based on a microbial model, knowing what aspects of microbial swimming are behaviorally controlled will be critical.

To that end, Arratia's group is developing two types of artificial cilia, a passive responder and an active responder, to determine whether these different modes of response affect swimming.

Another future step will be to understand whether the swim behavior of groups differs from that of individuals.

"For this study, we only looked at one alga swimming at a time," Arratia said. "We'd also like to know what would happen if you had a denser suspension of them, whether there would be collective swarming behavior, for instance."

Arratia, who has studied complex fluids for years, sees living fluids as an exciting new research direction.

"Anyone who has tried to get ketchup out of a bottle can appreciate how different complex fluids are from water," Arratia said. "These differences are caused by polymers and particles. Living fluids are also suspensions of particles in water, but now the particles are alive. That raises many interesting questions about even their most fundamental properties."

###

This research was supported by the National Science Foundation through grant DMR-1104705.

Media Contact

Evan Lerner
elerner@upenn.edu
215-573-6604

 @Penn

http://www.upenn.edu/pennnews 

Evan Lerner | EurekAlert!

More articles from Life Sciences:

nachricht Repairing damaged hearts with self-healing heart cells
22.08.2017 | National University Health System

nachricht Biochemical 'fingerprints' reveal diabetes progression
22.08.2017 | Umea University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

Cholesterol-lowering drugs may fight infectious disease

22.08.2017 | Health and Medicine

Meter-sized single-crystal graphene growth becomes possible

22.08.2017 | Materials Sciences

Repairing damaged hearts with self-healing heart cells

22.08.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>